1. Field of the Invention
The present invention relates to a fan arranged to produce an axial air current.
2. Description of the Related Art
A housing of a fan disclosed in FIGS. 9 and 10 of WO 2003/075433 has a structure in which two segments thereof are in contact with each other on a lower side of fan blades. The radial thickness of the housing is uniform with respect to an axial direction and a circumferential direction. Both the inside diameter and the outside diameter of the housing gradually increase with decreasing height.
In a casing of a fan disclosed in JP 2003-532026, an inner shell portion is used as a guide surface. The guide surface has the shape of a truncated cone, increasing in diameter with decreasing height, except in an inlet portion thereof. An end edge of each of a plurality of blades extends along the guide surface with a clearance space defined between the end edge and the guide surface. The casing is made up of a radially inner portion and a radially outer portion.
In the case where, as disclosed in WO 2003/075433, the diameter of an inner circumferential surface of a housing is arranged to increase from an inlet side toward an outlet side, and an outer circumferential edge of each blade is arranged to spread radially outward as it extends from the inlet side toward the outlet side, the housing is sometimes constructed of upper and lower segments which are capable of being detached from each other in order to prevent interference between the housing and any blade during an assembling process. However, when the housing is constructed of the upper and lower segments which are capable of being detached from each other, it is difficult to provide a fastening structure for fitting the upper and lower segments to each other while also achieving a small size of the housing. Accordingly, in the fan disclosed in FIGS. 9 and 10 of WO 2003/075433, the fastening structure is not provided, and each of the upper and lower segments of the housing is fixed to a fan installation location through screws. Such a structure, however, does not allow the fan to be treated as a single device, which makes an operation of installing the fan troublesome.